1. Field
A method is disclosed for installing port liners in a cylinder head of an internal combustion engine, and more particularly to a method for installing port liners in the exhaust ports of a cast cylinder head using a tube hydroforming process which results in a cylinder head with hydroformed exhaust port liners.
2. Description of the Related Art
Current methods for forming exhaust ports in an internal combustion engine typically involve casting a cylinder head with single walled exhaust ports. When an engine with this cylinder head design is operating, the exhaust gases exiting the combustion chamber flow through the exhaust port in the cylinder head and lose a significant amount of heat energy. This heat energy is wasted instead of being used to power turbomachinery or for rapid heating of the catalytic converter. Additionally, the engine's cooling system is taxed with removing this waste heat. These results are undesirable. Higher temperatures of the exhaust gases provide for more efficient operation of the catalytic converter which results in lower emissions. Reducing heat transfer of the exhaust gases to the cooling system of the engine allows for a lower coolant system load, that is, radiator size.
Consequently, it is known in this art to install exhaust port liners with a simple straight or curved configuration in the exhaust port or passage of a cylinder head of an internal combustion engine for the purpose of reducing heat transfer between the engine cooling fluid and the exhaust gas. The exhaust port liner maintains the elevated temperature of the exhaust gas, and decreases the rate of heat transfer to the cooling system creating an insulation layer between the exhaust gas and coolant passages in the cylinder head. This reduces the coolant system load and increases the exhaust gas temperature, potentially for recovery in a turbocharger, if so equipped, and maintains higher temperatures of the exhaust gas for more efficient operation of the catalytic converter, especially during engine starting.
There are instances where it may be desirable to use port liners for the intake ports in a cylinder head such as for reducing undesirable heating of the combustion air during the intake process. Lower combustion air temperature improves emissions, knock tolerance, and improves air charge density. Positioning port liners in the intake ports of a cylinder head can be difficult due to the irregular shape or non-uniform diameter of the passage. In recent designs of cylinder heads, the intake ports have complex shapes and cross-sections for the purpose of promoting charge motion in the cylinder. Fitting a port liner within these types of intake ports can be problematic.
There still exists a need for a method of installing port liners in cast cylinder heads. The method should not require any extra machining or boring of the cylinder ports. There is also a need for a method to install port liners in ports that have irregular shapes or non-uniform diameters. The port liner should provide an air gap over a major portion of the liner surface as an insulation barrier for maintaining the elevated temperature of the exhaust gas for an exhaust port, or for reducing undesirable charge air heating of the incoming air for combustion for an intake port.